Please see citations in the review

An exciting topic for future research!

/end

We also propose that these MTL connections may influence the emergence/separation of the 2 networks, DN-A and DN-B, during development/evolution:

Early spontaneous patterned activity within the MTL (e.g., traveling waves?) could 'tether' connected cortical regions into distinct networks:

We argue that these MTL connections help explain why these adjacent cortical networks have distinct functions:

🧠 DN-A supports episodic thinking through its prominent connections to parahippocampal circuits

🧠 DN-B supports theory of mind through its prominent connections to amygdala circuits

Recent work has demonstrated that these two networks are connected to distinct portions of the medial temporal lobe (MTL):

DN-A is connected to the parahippocampal cortex
DN-B is connected to the amygdala

Both networks appear to be in the anterior hippocampus, subiculum and entorhinal cortex

The two networks, DN-A and DN-B, support different forms of introspective thought.

DN-A is involved in recollection/prospection (e.g., thinking about the past or future)

DN-B is involved in theory of mind (e.g., thinking about someone else's thoughts).

Recently, individual-level "precision fMRI" has shown that the DN actually comprises multiple distinct networks (see image above)

The individualized network maps show much clearer separation between functions, suggesting that the overlap might have been a consequence of blurring in grouped data

Group-level estimates of the default network (DN) have long argued that it serves many introspective functions, including mentalizing (thinking about other people's thoughts, feelings & beliefs) and recollection/prospection.

Often noted was the heterogeneity but also overlap of functions in the DN:

Congratulations to you both! 👏🏽

Tagging co-authors:
@josephsalvo.bsky.social
Maya Lakshman
@aniaholubecki.bsky.social
@zeynepsaygin.bsky.social
Marsel Mesulam

...whatever the visual properties of those things.

Our work suggests that this specialization is shaped by connections to large-scale brain networks that aren't visual

So the interplay between visual and non-visual networks seems to shape the specialization of these late-stage visual areas

Excellent Q - see the paper below about how the specialization in this part of the brain is influenced by early life experience:
www.nature.com/articles/nn....

Could be this part of the brain specializes for processing visual things that are behaviorally important:
arxiv.org/abs/2411.08251

We welcome feedback - Read the full preprint here:
👉 www.biorxiv.org/content/10.1...

And congrats to Joe Salvo and the team for a careful and comprehensive (5y+) study!

🧵 The end

We propose that thinking about this region a “nexus”, or a hand-off point, between visual and transmodal language systems, is useful for understanding why it is so critical for reading.

We think this can help us understand the weird properties of the VWFA: it shows a mixture of responses (visual, speech) because it is at the confluence of two brain systems: the transmodal LANG network and unimodal (orthographic) visual stream.

Conclusion: Our results support that the network connections to LANG can explain functional differences along the ventral visual stream.

More anterior stream = more transmodal, more selective for word-like visual input
More posterior stream = more visual, less discriminant about visual stimuli

This suggests that the basal LANG region seems to care about visual stimuli that look like they might be words and readable

AND – we replicated that familiar (Roman) letter strings activate the whole orthographic stream, but in contrast, strings of numbers only activated the more posterior regions!

This was very surprising – numbers are also highly learned, yet their activity is like the foreign scripts map above:

Using the NSD fLOC task data, we replicated that the anterior part of the orthographic stream (teal) converges on that basal LANG region: